A receiver may be tuned to demodulate one channel out of many channels which make up a radio frequency (RF) signal band. A channel selection process in, for example, a receiver, may typically be accomplished by using one or more mixing operations and filters. Because it may be difficult to design a highly selective channel filter at an RF carrier frequency, the mixing operations may typically be preceded by a less selective band-select filter with a wide passband that encompasses the entire signal band. After demodulation with a mixer, a low-pass channel-select antialiasing filter and an analog-to-digital converter (ADC) may digitize the channel signal. The components of the receiver before the mixer may be referred to as “RF front-end” components and the components after the mixer may be referred to as “baseband” components of the receiver.
Because real-life components of RF receivers may not be perfectly linear, one or more components in the signal chain of a receiver may add some nonlinear distortion. In other words, a component may artificially add frequencies to an output signal of that component. The artificially added frequencies did not originally exist at the component's input signal. For example, if a component with 2nd-order distortion has a pair of tones at its input with frequencies f1 and f2, then the signal at the component's output may exhibit not only the original tones at f1 and f2, but also intermodulation products which are created at frequencies which are combinations of the original input frequencies (e.g., 0, 2*f1, 2*f2, f1+f2, and f131 f2). It is important to recognize that intermodulation products may fall at frequencies different than the original tones which created them.
Because intermodulation products may fall at frequencies different than the original tones which created them, nonlinear RF front-end components can create in-channel intermodulation products in response to out-of-channel signals. This type of distortion may detrimentally decrease the receiver's spurious-free dynamic range (SFDR) because there may be no inherent way to distinguish the intermodulation products from the desired signals. As a result, there may be a need to identify such intermodulation products and remove them to maintain RF signal integrity in receivers.